The present invention relates to the inhibiting and preventing corrosion of iron based metals which are in contact with aqueous systems, such as cooling water systems.
Iron and iron metal containing alloys such as mild steel are well known materials used in the construction of apparatus in which aqueous systems circulate, contact the iron based metal surface and may be concentrated, such as by evaporation of a portion of the water from the system. Even though such metals are readily subject to corrosion in such environments, they are used over other metals due to the strength they have.
It is known that various materials which are naturally or synthetically occurring in the aqueous systems, especially such systems formed from natural resources such as seawater, rivers, lakes and the like, attack iron based metals (the term "iron based metals" shall mean in the present disclosure and the appended claims iron metal and metal alloys containing iron therein). This is especially true where the aqueous system is a hard water i.e. contains about 300 ppm or greater of calcium and magnesium therein.
Typical apparatus in which the iron metal parts are subject to corrosion include evaporators, single and multi-pass cooling towers and associated equipment and the like. As the aqueous system passes through or over the apparatus a portion of the aqueous system evaporates causing a concentration of the materials contained in the system. These dissolved materials approach and reach a concentration at which they cause severe pitting and corrosion which eventually requires replacement of the metal parts.
Various corrosion inhibitors have been previously used. These include inorganic nitrite or phosphate salts and the like. These materials have only minor inhibiting effects and tend to decompose when used in environs such as encountered in cooling towers, evaporators and similar apparatus wherein the aqueous system is subjected to elevated temperatures.
Copolymers such as described with respect to the present invention have been found, when used alone, to have substantially no corrosion inhibiting effect.
It is desired to have a composition and a method capable of being easily worked which substantially inhibits the corrosion of iron based metals. It is desired to have a composition capable of substantially inhibiting corrosion of iron base metals of apparatus in contact with aqueous systems which tend to concentrate. It is further desired to have a composition which is capable of inhibiting corrosion when used at very lower dosages.